Alexandrite is a very rare (and very expensive) variety of gem-quality chrysoberyl. Although most people have probably never seen a natural alexandrite, this gemstone has replaced the traditional pearl as the modern June birthstone. Its glamorous history and beauty have likely contributed to its mystique in the public imagination. Alexandrites are well-known for displaying one of the most remarkable color changes in nature. “Emerald by day, ruby by night,” the most desired and well-cut stones are green in sunlight and red in incandescent light. This is an excellent jewelry stone (if you can acquire one).
There are two primary drivers of alexandrite's value. First, the closer the colors are to pure green and red, the higher the value. Second, the more distinct the color change, the higher the value. Alexandrite can exhibit everything from 100% to just 5% color change. Thus, the most valuable alexandrite gems would have a 100% color shift from pure green to pure red.
However, an alexandrite's color change has more effect on its value than its clarity. For example, take two gems, each weighing a half-carat. One gem is eye clean, with a 50% brownish/red to greenish/blue color change. The other is an opaque cab with a 100% green to red color change. The opaque cab would be considered higher in value.
Size is always a significant factor in value. The largest known faceted alexandrite is a red/green color change stone weighing in at 65.7 carats. This gem from Sri Lanka resides at the Smithsonian Institution. The largest Russian gems are about 30 carats. However, the vast majority of alexandrites are under one carat. You can see this reflected in our Price Guide. In sizes up to one carat, top-quality natural gems sell for $15,000. Over one carat, the prices range from $50,000 to $70,000 per carat.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Is a Variety of||Chrysoberyl|
|Refractive Index||1.746 – 1.755|
|Colors||Varies in color with incident light: green, blue-green, or pale green in daylight; mauve, violet to red, purplish in incandescent light.|
|Fracture||Weak conchoidal to uneven, brittle|
|Specific Gravity||3.68 – 3.80|
|Birefringence||0.008 – 0.010|
|Cleavage||Distinct to poor, 1 direction|
|Luminescence||Weak red in SW and LW|
|Spectral||Narrow doublet at 6805/6875, with weak, narrow lines at 6650, 6550, and 6490 and broad band at 6400-5550. Total absorption below 4700.|
|Special Care Instructions||None|
|Transparency||Opaque to transparent|
|Phenomena||Color change, chatoyancy (very rare)|
|Formula||BeAl2O4 + Cr|
|Pleochroism||Deep red/orange-yellow/green. (Myanmar gems anomalous: purple/grass-green/blue-green).|
|Optics||See “Identifying Characteristics” below. Biaxial (+), may also be (–), 2V= 70°.|
|Etymology||Named after Czar Alexander II of Russia.|
|Occurrence||Occurs in pegmatites, gneiss, mica schist, dolomitic marbles; also found as stream pebbles and detrital grains.|
Alexandrite was discovered in the Ural Mountains of Russia in the 1830s. Noted mineralogist Nils Gustaf Nordenskiöld was the first to realize this unusual green, color-changing gemstone was something new. The stone was named by Count Lev Alekseevich Perovskii in 1834, in honor of the then future Czar of Russia, Alexander II. This association with the Czars likely helped the gem gain celebrity by association. In the 19th and early 20th centuries, as historian David Cannadine notes, the Czars were widely considered the standard for royal pomp (a position the British Royal Family has enjoyed more recently).
If not for its name, the circumstances necessary for the formation of natural alexandrite and its mining history might have ensured the gem would be extremely rare as well as little known. To form, alexandrite requires both beryllium (Be), one of the rarest elements on Earth, and chromium (Cr). (These are also required for emerald creation). However, these elements rarely occur in the same rocks or in geological conditions where they interact. Furthermore, the original source of alexandrites was almost exhausted after only a few decades of mining. Since the 1980s, more sources have been located.
Chrysoberyls are well-known as “cat’s eye” gems. Alexandrites that show a cat’s eye effect are quite rare.
Brazilian alexandrites tend to have pale colors, pale mauve to pale blue-green, but finer gems have been found recently in limited quantity. Substantial amounts (1,200 ppm) of the element gallium (Ga) replacing aluminum (Al) have been detected in some Brazilian material. Sri Lankan alexandrite is often deep olive-green in sunlight, whereas Russian stones are blueish green in sunlight. Zimbabwean gems are a fine, emerald-green color in sunlight but are usually tiny (under 1 carat) if clean. The color change in Zimbabwean gems is among the best known. It’s a shame that large, clean stones are virtually unobtainable from the rough from this locality.
Some properties of alexandrites vary according to their source.
|Properties of Alexandrite from Various Localities|
|Specific Gravity||–||–||3.71||3.68||3.64 – 3.80|
There is a considerable market for synthetic alexandrite, which was first created in the 1960s. Alexandrites can be grown through melt, hydrothermal, or flux methods in a lab. These synthetic stones have the same chemical and physical properties as natural alexandrites. They are real alexandrites but not natural. Although the synthetics are far less expensive than their natural counterparts, they’re still among the most expensive synthetic gemstones available.
Synthetic alexandrite can sometimes be identified by inclusions caused by various growth procedures. Melt techniques, like the Czochralski, can created curved striae. Hydrothermal growth can create bubbles and liquid inclusions. Flux methods can leave inclusions of platinum or other seed materials.
There is also a considerable market for lookalikes or simulants. These can range from synthetic corundum with alexandrite-like color change (produced very inexpensively) to actual, natural color-change chrysoberyl stones. Although alexandrite is a variety of chrysoberyl, not all color-change chrysoberyls are alexandrites. These gems also command a high price, but, again, not nearly as high as alexandrites. (Editor’s Note: There is no gemological consensus for restricting the definition of alexandrite to color-change chrysoberyl gems with a limited, “classic” range of color shift).
Buyer beware. If you find an alexandrite at a relatively bargain price, it’s likely not natural and possibly not an alexandrite. A professional gemological laboratory can make a determination.
Natural alexandrites usually don’t receive any treatments.
Mines in the Urals have re-opened but only produce a few carats of gem quality material each year. In 1987, alexandrite was found in Brazil. Later, the gemstone was discovered in Madagascar, Myanmar, Sri Lanka, and Zimbabwe. However, none of these sites produce as rich and vivid a color change as the original Russian source. The main source of large, natural alexandrite gems today is antique jewelry.
Stones over five carats are very rare, especially with good color change.
- Smithsonian Institution (Washington, DC): 65.7 cts (Sri Lanka).
- British Museum of Natural History (London): 43 and 27.5 cts (Sri Lanka).
- Institute of Mines (St. Petersburg, Russia): cluster of three crystals, 6 x 3 cm (Urals).
- Fersman Museum (Moscow, Russia): crystal group, 25 x 15 cm, crystals up to 6 x 3 cm (Urals).
- Private Collections: stones up to 50 cts have been reported.
With a hardness of 8.5, alexandrite is a very durable stone suitable for any jewelry setting. (Care should be taken when faceting the stone, since it’s sensitive to knocks and extreme heat). No special care is required for alexandrites. They can be cleaned mechanically, per the instructions of the machine to be used, or, of course, with warm, soapy water and a brush. Consult our gemstone jewelry cleaning guide for more information.